This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-375041, filed Dec. 28, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a misalignment inspection method, a charge beam exposure method, and a substrate for pattern observation, and particularly to a misalignment inspection method for a semiconductor device pattern, a charge beam exposure method, and a substrate for pattern observation.
In inspection of a lithography process in the manufacture of micro semiconductor devices, the precision of pattern dimensions and misalignment are measured. The inspection of dimensions and that of misalignment are conventionally achieved by separate devices, respectively, which result in high device costs and take a long time for the inspections.
A method using a scanning electron microscope (SEM) has been being widely used for inspection of pattern dimensions. Meanwhile, several methods using also the SEM to measure misalignment have been proposed. For example, U.S. Pat. No. 2,616,676 discloses a method in which a micro inspection mark is used to carry out simultaneously length measurement and alignment inspection. Also, Proc. SPIE 1673 pp157-164 (1992) discloses a method in which a gap structure is provided for a reference mark (first mark) on a lower layer and a second mark is formed thereof of a resist, thereby to so that a relative positional difference between both marks.
Also, in conventional techniques, the ground position is difficult to detect if a ground mark taken as a reference for misalignment measurement is flattened as a result of film formation and polishing process in the course of manufacturing process. In the case where the reference mark is flattened, the ground mark and its periphery are electrified and a potential contrast image based on the difference between their surface potentials is used under the irradiation condition that the current amount is larger and the acceleration voltage is set higher compared with a normal length. As a result, the ground mark can be measured. However, the asymmetry and peripheral structure of a mark greatly influences the charging thereby causing measurement errors in the method of applying intentionally charges to a sample. In particular, a phenomenon of excessive charge-up occurs with respect to a mark on an upper layer, leading to a problem that the relative position thereof cannot be measured correctly in relation to the ground mark.
Further, there is a further problem that offset may occur in measurement results if a beam is scanned in parallel with the misalignment measurement direction.
As described above, in the method of using a contrast image based on a difference between surface potentials in a conventional micro pattern inspection method, charges are intentionally applied so that the asymmetry and peripheral structure of a mark greatly influence the charges, thereby causing measurement errors. In particular, there is a problem that the phenomenon of excessive charge-up is caused with respect to the mark in an upper layer, so the relative position relative to a ground cannot be measured correctly. In addition, there is another problem that offset may occur in measurement results if a beam is scanned in parallel with the misalignment measurement direction.
An object of the present invention is to provide a misalignment inspection method, a charge beam exposure method, and a substrate for pattern observation, which enable more precise misalignment inspection.
A misalignment inspection method according to the present invention is characterized by comprising: a step of scanning an area with a charge beam, the area including a part of first and second marks in a sample including the first mark and the second mark which is formed in a layer upper than the first mark and is used for measuring a relative position relative to the first mark, on a substrate, and the first and second mark being arranged so as not to have an area overlapping each other in a measurement direction in which relative positions of the first and second marks are measured; a step of detecting first charged particles from the sample on a line including the first mark; a step of detecting second charged particles from the sample on a line including the second mark; a step of obtaining representative points of the first and second marks, based on signal waveforms obtained from the first and second charged particles, respectively; and a step of calculating a positional misalignment amount of the first and second marks, based on the representative points of the first and second marks.
Another misalignment inspection method according to the present invention comprising: a step of scanning an area with a charge beam, the area including a part of first and second marks in a sample including the first mark and the second mark which is formed in a layer upper than the first mark and is used for measuring relative positions of the first and second marks, on a substrate, by operating the charge beam in a direction vertical to a measurement direction in which relative positions of the first and second marks are measured, thereby to detect charged particles and to obtain a signal waveform as a positional function; a step of respectively detecting representative positions of the first and second marks, based on the signal waveform; and a step of calculating a positional misalignment amount of the first and second marks, based on the representative positions of the first and second marks.
Preferably, a flat layer having a flat surface is formed on the substrate including the first mark, the second mark is formed on the flat layer, and the second mark is exposed from a surface of the sample.
A charge beam exposure method according to the present invention is characterized in that the scanning with the charge beam is performed by a charge beam exposure device, and position-aligned charge beam exposure is carried out on the basis of a calculated position misalignment amount of the first and second mark.
Preferably, the first and second marks are line patterns.
In the present invention, positions of first and second marks in an used sample are arranged at positions where the marks do not overlap in the direction in which misalignment measurement is performed, in case of making the misalignment inspection with use of a sample in which first and second misalignment inspection marks are respectively formed in different layers.
As a result, signal waveforms are individually obtained with respect to the first and second marks, respectively, in case of making the misalignment measurement. Therefore, inspection can be achieved with reduced influence from charge-up of the second mark, which will be caused in case that scanning is performed in one single direction. Accordingly, misalignment inspection can be achieved with higher precision.
Also, in the present invention, signal waveforms are obtained by scanning with a charge beam in a direction vertical to the misalignment measurement direction. Accordingly, inspection can be achieved without influences from offset which will be caused in the case where the scanning direction of the charge beam overlaps the misalignment measurement direction. Accordingly, more precise misalignment inspection can be achieved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.